Fig. 2: Bi-circular and linear polarization rotation scans for quartz and MgO.

a–c The yield of the eighth harmonic order (H8) as a function of the rotation angle of the threefold field. d–f Yield of H8 as a function of linear polarization angle. For MgO, H8 from linearly polarized drivers is symmetry-forbidden, hence H9 is presented.